In electronic parts, e.g., semiconductor devices, tapered metal bumps composed of, for example, gold are formed at ends of wiring patterns, which are composed of copper and formed on one side surface of a substrate composed of plastic, ceramic, etc., for being connected to other electronic parts. For example, a method of forming a tapered metal bump by a gas deposition process is disclosed in Patent Document 1.
The disclosed method is shown in FIG. 14. In the method shown in FIG. 14, a resin mask layer 204 covering wiring patterns 202, 202 . . . formed on one side surface of a substrate 200 is patterned, holes 206 in which the wiring patterns 202 are exposed in the bottom surfaces are formed, and then the substrate 200 is mounted on a movable stage 208 as shown in FIG. 14A.
Next, as shown in FIG. 14A, the movable stage 208 is continuously moved from side to side in a direction X, and metal nanoparticles produced by a gas deposition system are ejected from a large diameter nozzle 210, whose diameter is larger than inner diameters of the holes 206, toward the holes 206, 206 . . . .
The metal nanoparticles ejected from the nozzle 210 deposit on the mask layer 204 and form a deposited layer 212, further they deposit in the bottom surfaces of the holes 206, 206 . . . and form metal bumps 214, whose top surfaces are nearly flat.
Then, ejecting the metal nanoparticles from the large diameter nozzle 210 is stopped, and thereafter the metal nanoparticles are ejected from a small diameter nozzle 216, whose diameter is smaller than the inner diameters of the holes 206, toward the top surfaces of the metal bumps 214 formed in the selected holes 206 of the holes 206, 206 . . . which have been formed on the one side surface of the still substrate 200. The metal nanoparticles ejected from the small diameter nozzle 216 deposit on the flat top surfaces of the metal bumps 218 and form the tapered metal bumps 218.
Patent Document 1: Japanese Patent Kokai Gazette No. 2002-184804